The present invention relates generally to probe adapters for measurement probes and more particularly to a probe tip adapter usable with very high frequency single ended and differential measurement probes.
Probe tip adapters are accessories developed for measurement probes to allow probing of various types of electrical components. The adapters allow connections to square pins mounted on a circuit board, ground points on the circuit board, leads of surface mounted integrated circuit devices, and the like. The P6243 Active Measurement Probe 10, manufactured and sold by Tektronix, Inc., Beaverton, Oreg. and assignee of the instant invention, has a socket type probe tip 12 and ground socket 14 as shown in FIG. 1 and depicted in design patent DES 354,923. The socket tip has an overall length of 0.255 inches and a diameter of 0.065 inches. The socket bore has a diameter of 0.038 inches and a length of 0.225 inches. Various types of probe Up adapters are inserted into the socket to allow various types of probing.
A positioning aid probe tip adapter 16, described in U.S. Pat. No. 5,387,872, has a housing 18 with a central bore 20 there through that receives a probing tip 22. The housing 18 has teeth formed in one end defining slots 24 that are positionable between the leads of an integrated circuit device. The bore 20 extends into one of these slots 24 with the probing tip 22 exposed therein. The other end of the probing tip 22 extending from the other end of the housing 18 contact shaft for insertion into the socket type probe tip 12. A standard probing tip 26 has a shaft 28 that has one end tapering to a point 30 for probing IC leads, points on a circuit board and the like. The other end of the shaft is inserted into the socket type probe tip 12. The probing tip 26 may also include a cone shaped protrusion 32 formed on the shaft 28 for abutting against the socket type probe tip 12. Adapter 34 is an assembly having a flexible electrically conductive lead 36 attached to an electrical contact shaft 38 that is inserted into the socket type probe tip 12. Adapter 40 has a square pin socket 42 on one end and a contact shaft 44 on the other for inserting into the probe tip 12. The contact shafts for the above described adapters have a length in the range of 0.250 inches.
The above described probe tip adapters may also be used with differential type probes, such as the P6246 Differential Probe 50, manufactured and sold by Tektronix, Inc., Beaverton, Oregon, the assignee of the instant invention and shown in FIG. 2. The differential probe 50 has a measurement probe head 52 with dual socket type probing tips 54, 56 extending from the nose of the probe head 52. When used with a differential probe, the adapters are generally ganged together for ease of use. For example, two flexible electrically conductive lead adapters are positioned in a trapezoidal shaped housing 58 with the flexible electrically conductive leads 60, 62 extending from one end of the housing 58 and the contact shafts 64, 66 extending from the other end of the housing. The flexible electrically conductive leads 60, 62 have a pitch geometry compatible with the leads of surface mounted integrated circuit devices and the contact shafts 64, 66 have a pitch geometry compatible with the socket type probe tips 54, 56 of the measurement probe head 52. Such a probe tip adapter is described in co-pending patent application Ser. No. 08/738,861, filed Oct. 26, 1996 and assigned to the assignee of the instant invention. Offset probing tips 70, 72 are ganged together with an insulating material 74, such as plastic, having bores formed therein that receives the probing tips 70, 72. The bores have a center to center spacing or pitch geometry that provides the contact shafts 76, 78 with a pitch geometry compatible with the socket type probing tips 54, 56. The respective probing tips 70, 72 have bends 80, 82 formed in them to offset the probing tips 84, 86 to allow the probing tips to match various pitch geometries of surface mounted integrated circuit devices. Each offset probing tip 70, 72 may be secured in the insulating material 74 by forming outwardly extending rib on the probing tip shaft that engage the interior surface of the bore in the insulating material 74 into which it is inserted. Alternately, each probing tips 70, 72 may be provided with a small keeper that is slid onto the probing tips after the probe is inserted into the insulating member 74 and abuts the insulating material 74. The keepers are frictionally held in place of the probing tips. The offset probing tips 70, 72 may also be rotatable within the insulating material 74 to allow the pitch geometry of the probing tip to be changed to match the pitch geometry of the integrated circuit device. The differential square pin adapter 90 has a housing 92 having contact shafts 94, 96 extending from one end that are compatible with the pitch geometry of the differential probe tips 54, 56. Extending from the other end of the housing 92 are wires 98, 100 that are attached to the square pin sockets 102, 104. The differential probe also has a tip saver adapter 110 that fits over the nose of the differential probe head 52. The tip saver 110 has contact shafts 112, 114 extending into a cavity 116 formed in the tip saver 110. The nose of the measurement probe head fits into the tip saver cavity 116 with the contact shafts 112, 114 being inserted into the socket type probe tips 54, 56 of the probe head. Each contact shaft is connected to socket type probe tip 118, 120 that are identical to the probe tip sockets of the measurement probe head. This adapter 110 prevents excessive wear and damage to the socket type probe tips 54, 56 of the probe head. Excessive wear and damage to the socket type probe tips of the measurement probe head requires the replacement of the head.
Probe tip capacitance and inductance are major drawback to using socket type probe tip or tips in measurement probes. Tip capacitance and inductance limits the input bandwidth of the probe. With the electronic industry continuing to develop integrated and hybrid circuits operating at higher and higher frequencies, a new type of measurement probe design is required that has substantially reduced probe tip capacitance and inductance. This requires reducing the probe tip length and diameter. Likewise, probe tip adapters are required for these low capacitance measurement probes that have reduced length and diameter. Such probe tip adapters of necessity need to be very small in size. However, such small size adapters could be easily lost.
What is needed is a probe tip adapter that is compatible with a low capacitance measurement probe. The adapter should be adaptable to various types of configurations while minimizing as much as possible additional probe tip capacitance and inductance by reducing the length and diameter of the adapters. The adapter should also be attachable to the low capacitance probe tip of the probe over repeated cycles without losing physical or electrical connectivity. Further, the probe tip adapter should have some form of holder to prevent the loss of the adapters due to their small size.
Accordingly, the present invention is to a probe tip adapter for a measurement probe wherein the probe has at least a first probing tip extending from the measurement probe. The probe tip adapter has at least a first electrically conductive element with a bore at one end and a probing contact formed on the other end. Disposed in the bore of the electrically conductive element is an electrically conductive elastomer having sufficient tensile strength, compression set, hardness, deflection force, elongation and percent recovery for repeatably securing the electrically conductive element to the probing tip of the measurement probe. An element holder is positionable on the measurement probe and has a cavity formed in one end for receiving the measurement probe. At least a first bore is formed in the other end of the element holder that extends to the cavity and is aligned with the probing tip of the measurement probe. The electrically conductive element is positioned in the holder bore such that the probing tip penetrates the elastomer and the probing contact extends from the holder.
The electrically conductive element is preferably machined as a single part with a first portion associated with the bore end of the element and a second portion associated with the probing contact end of the element. Each portion has a perimeter with the perimeter of the first portion being smaller than the perimeter of the second portion forming an outward extending shoulder from the first portion for abutting against the holder. Alternately, the electrically conductive element may be formed with a first electrically conductive member associated with the bore end of the element and a second electrically conductive member associated with the probing contact end of the element that are joined together. Each member has a perimeter with the perimeter of the first member being smaller than the perimeter of the second member to form an outwardly extending shoulder from the first member for abutting against the holder.
The probing contact of the second portion or member may be configured with a shaft that tapers at one end to a point and the other end that forms a cone extending outward from the shaft having a perimeter larger than the perimeter of the first portion. The shaft of the probing contact may further be angled. The second portion of the probing contact may also be configured with a bore formed therein that receives a spring contact where the probing contact bore and the spring contact are dimensioned to receive a 0.025 inch square pin. The electrically conductive element preferably has an outwardly extending rib formed on the bore end of the element that engages the bore of the holder. The element holder includes a mechanical attachment facility including at least a first pair of nesting detent elements disposed in the cavity and in the measurement probe with one of the nesting detent elements formed in the cavity and the other of the nesting detent elements formed on the measurement probe. The nesting detent elements may be configured as a knob and a depression, a rib and a channel or the like.
The probe tip adapter is usable with both a single ended measurement probe and a differential measurement probe. When used with a differential probe, probe tip adapter has a second electrically conductive element with electrically conductive elastomer disposed in the bore. The element holder has a second bore formed therein extending to the cavity and aligned with the second probing tip of the differential probe. The second electrically conductive element is positioned in the second holder bore such that the second probing Up penetrates the elastomer of the second electrically conductive element and the probing contact of the second element extends from the holder. The angled probe tips of the electrically conductive elements may also be laterally movable from at least a first position having a first pitch geometry to a second position having a second pitch geometry.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.